Optical disc device and optical disc discriminating method

ABSTRACT

An optical disc device includes a laser light source for radiating a laser light beam illuminated via an objective lens on a signal surface of an optical disc, a return light detection unit for detecting the reflected light radiated from the laser light source and reflected from the signal surface of the optical disc, a disc discriminating unit for discriminating the type of the optical disc based on a detection output of the return light detection unit, a unit for detecting tracking error signals of plural different types of different detection systems based on the detection output of the return light detection unit, a tracking unit for displacing the objective lens along the radius of the optical disc responsive to the tracking error signals for tracking-controlling a laser spot of the laser light focussed on the signal surface of the optical disc and a controlling unit for switching the detection system based on a discriminating output by the disc discriminating unit for selecting one of the plural types of the tracking error signals responsive to the types of the optical discs.

This is a divisional of application Ser. No. 09/003,933, filed Jan. 7,1998, now U.S. Pat. No. 6,147,941.

BACKGROUND OF THE INVENTION

1. Field of the invention

This invention relates to an optical disc device capable of coping withplural types of optical discs, and a method for discriminating betweenplural types of optical discs.

2. Description of Related Art

As optical discs are in widespread use, optical discs of the compactdisc CD type are used in many fields, including the field of musicalapplications. The CDs for music are usually designed as replay-onlymedia. However, an overwrite type disc termed compact disc recordable(CD-R) is also commercialized.

On the other hand, an optical disc termed a digital versatiledisc/digital video disc (DVD) has also been developed as an optical discsuitable for multimedia use. This DVD is proposed as being adaptable toa wide field of applications, such as for use with video data, audiodata or computer data. The DVD, which is an optical disc of the samesize as the CD (12 cm in diameter), has a significantly increasedrecording capacity.

Meanwhile, in keeping pace with the development of a new optical disc,it becomes desirable to provide an optical disc device that is alsocompatible with a conventional optical disc.

As for the DVD, it is desirable to develop an optical disc devicecapable of coping with both the CD and the DVD. However, since the CDand the DVD differ in reflectivity depending on, for example, adifference in the structure of the signal recording layer of the opticaldisc, the RF signals obtained by an optical pickup are varied in signallevel, depending on the optical disc type, whilst optimum values ofparameters of various servo systems, such as focussing servo or trackingservo systems, are also changed.

Therefore, an optical disc device, adapted for coping with pluraloptical disc types, is required to correctly discriminate the type ofthe optical disc on loading the optical disc thereon.

If the disc is of the type in which an optical disc is housed in acartridge, the disc type can be easily discriminated by providing acartridge discriminating hole. However, if the optical disc is not ofthe type housed in a cartridge, and moreover the optical disc itself isof the same size, this mechanical discrimination system cannot be used.

Moreover, if special components or units are provided for discriminatingthe disc type, such as a sensor, the device is undesirably complicatedin structure, while the manufacturing costs are also raised.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide an opticaldisc device and an optical disc discriminating method in which pluraloptical disc types having different numbers of signal recording layersare discriminated and an operating mode corresponding to the opticaldisc type is set by control means based on the discriminating output forreliable reproduction from the plural types of the optical discs.

The present invention provides an optical disc device including a laserlight source for radiating a laser light beam illuminated via anobjective lens on a signal surface of an optical disc, a return lightdetection unit for detecting the reflected light radiated from the laserlight source and reflected from the signal surface of the optical disc,a disc discriminating unit for discriminating the type of the opticaldisc based on a detection output of the return light detection unit, aunit for detecting tracking error signals of plural different types ofdifferent detection systems based on the detection output of the returnlight detection unit, a tracking unit for displacing the objective lensalong the radius of the optical disc responsive to the tracking errorsignals for tracking-controlling a laser spot of the laser lightfocussed on the signal surface of the optical disc and a controllingunit for switching the detection system based on a discriminating outputby the disc discriminating unit for selecting one of the plural types ofthe tracking error signals responsive to the types of the optical discs.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1C illustrates the structure of optical discs associated withan optical disc device embodying the invention.

FIG. 1 illustrates the structure of an optical disc associated with anoptical disc device embodying the invention.

FIG. 2 is a perspective view showing a mechanical deck of the opticaldisc device.

FIG. 3 is a block diagram showing the structure of the optical discdevice.

FIG. 4 is a schematic plan view of an eight-segment photodetector of theoptical disc device.

FIG. 5 is a block diagram showing the structure of a tracking block inthe optical disc device.

FIG. 6 illustrates the physical structure of a DVD-RW disc associatedwith the optical disc device.

FIG. 7 is a block diagram showing the structure of a third trackingerror signal generating block in the tracking block.

FIG. 8 is a circuit diagram showing the structure of a DPD filter in thethird tracking error signal generating block in the tracking block.

FIG. 9 is a graph showing the frequency response of the DPD filter ofFIG. 8.

FIG. 10 is a block diagram showing the structure of a mirror block inthe optical disc device.

FIGS. 11A-11D are waveform diagrams for illustrating the operation ofthe mirror block.

FIG. 12 is a block diagram showing the structure of a discriminationsignal generating block in the optical disc device.

FIG. 13 recruit diagram showing the structure of an APC circuit in theoptical disc device.

FIG. 14 is a graph showing gain characteristics of the APC circuit

FIG. 15 shows the relative position between a CD and an objective lensfor illustrating the operating principle of disc discrimination in theoptical disc device.

FIG. 16 shows the relative position between a DVD and an objective lensfor illustrating the operating principle of disc discrimination.

FIGS. 17A-17E are waveform diagrams of various signals for illustratingthe operating principle of discrimination.

FIG. 18 is a flowchart for illustrating the operation of discdiscrimination.

FIGS. 19A-19E are waveform diagrams showing a disc discrimination signalfor a singe-layer disc.

FIGS. 20A-20E are waveform diagrams showing a disc discrimination signalfor a double-layer disc.

FIG. 21 is for illustrating the sequence of operations fordiscriminating the single-layer disc and the double-layer disc by asystem controller in the optical disc device.

FIG. 22 is a flowchart for illustrating another example of theoperations for discriminating the disc types by a system controller inthe optical disc device.

FIG. 23 is a flowchart for illustrating the sequence of operations fordiscriminating the single-layer disc he double-layer disc in the exampleof the operations for discriminating the disc types by the systemcontroller of FIG. 22.

FIGS. 24A-24D are waveform diagrams for illustrating the discdiscrimination signal in the sequence of operations for discriminatingthe single-layer disc and the double-layer disc of FIG. 23.

DESCRIPTION OF PREFERRED EMBODIMENTS

Referring to the drawings, preferred embodiments for carrying out thepresent invention will be explained in detail.

The present invention is applied to an optical disc device associatedwith a CD and a DVD. Before proceeding to the explanation of the opticaldisc device embodying the invention, the structures of the CD, CD-R andthe DVD will be explained with reference to FIGS. 1a-1 c. Meanwhile, theCD, CD-R and the DVD are all discs 12 cm in diameter.

FIGS. 1a, 1 b and 1 c illustrate a layered structure as cross-sectionsof the CD, CD-R and the DVD. As shown in these figures, the overall discthickness of each of the CD, CD-R and the DVD is approximately 1.2 mm.

On the CD 100 shown in FIG. 1a, a disc substrate (transparent layer) 101is molded from a transparent synthetic resin material, such as atransparent polycarbonate resin, polyvinyl chloride or acrylic resin,having high light transmission, mechanical resistance and resistanceagainst chemicals. On a signal surface 102 of the disc substrate 101 aretranscribed pits by a stamper assembled into a mold die. These pits inthe signal surface 102 are formed in the disc substrate 101 as encodedorifices having different circumferential lengths in association withpre-set information signals for comprising a recording track. On thesurface of the disc substrate 101 carrying the signal surface 102 isdeposited aluminum having high light reflectance for forming areflective layer 103 as a signal recording layer. The entire assembly iscovered by a protective layer 104 for completing a CD 100.

On this CD 100, a laser light beam from a disc driving device isincident on the CD 100 from the disc surface 105 so that the informationrecorded on the signal surface 102 is detected from the reflected laserlight.

FIG. 1b shows a CD-R 110 which is a medium permitting overwriting. TheCD-R 110 has physical properties, such as diameter, weight and thicknessin common with the CD 100. However, the CD-R 110 can be manufacturedeconomically in smaller quantities and longer in durability than the CD100 and hence is suited for data storage.

On this CD-R 110 is also arranged a disc substrate (transparent layer)111 looking from the disc surface 116. On the disc substance 111 arelayered an organic dye layer 114, as a signal recording layer, a goldreflective layer 113 and a protective layer 115, in this order, forcompleting the CD-R 110. In this CD-R 110 is also formed a grooveoperating as a laser light illumination guide during recording and whichis covered by the organic dye layer 114.

Similarly, a DVD 120 shown in FIG. 1c has a disc substrate 121, from adisc surface 128, and a signal surface on the opposite side with respectto the disc substrate 121. Two types of the DVD, that is a DVD with asingle signal surface, termed a single-layer disc, and a DVD with adouble signal surface, termed a double-layer disc. FIG. 1c shows anexample of the double-layer disc. That is, a first data recording layeris formed by a first signal surface 122 and a first reflective layer 123associated with the first signal surface 122. A second data recordinglayer is formed by a second signal surface 124 and a second reflectivelayer 125 associated with the second signal surface 124. An adhesivesurface 126 is formed on the second reflective layer 125 and a dummysubstrate 127 is bonded by this adhesive surface 126.

The first reflective layer 123 is a semi-transparent film and isdesigned to reflect a pre-set proportion of the laser light. Thus, ifthe laser light is focussed on the first signal surface 122, the signalsrecorded on the first signal surface 122 can be read from the reflectedlight by the first reflective layer 123, whereas, if the laser light isfocussed on the second signal surface 124, the laser light istransmitted through the first reflective layer 123 to be converged onthe second signal surface 124, such that the signals recorded thereoncan be read out from the light reflected by the second reflective layer125.

In case of the single-layer disc, the signal surface and the reflectivelayer are formed similarly to the second signal surface 124 and thesecond reflective layer 125, respectively.

As may be seen from FIGS. 1a, 1 b and 1 c, the signal surfaces 102 and112 of the CD 100 and the CD-R 110 are formed at separations close tothe disc thickness from the disc surfaces 105, 116. That is, the signalsurfaces 102 and 112, on which to focus the laser spot, are separated byapproximately 1.2 mm from the disc surfaces 105, 116.

On the other hand, the signal surfaces 122 (124) of the DVD 120 are at amid-point of the disc thickness. That is, the signal surfaces 122 and124, on which the laser spot is focused, are separated by approximately0.6 mm from the disc surface 128. The recording density by pits formedon the signal surfaces 122 (124) is higher than that of the CD 100 andthe CD-R 110.

Due to this difference, laser light having a wavelength not larger than650 nm is used as the playback laser light. In addition, the numericalaperture (NA) of the objective lens is increased to 0.6, while theoptical pickup used is optimined for focussing the laser spot at aposition separated approximately 0.6 mm from the disc surface 128.

Meanwhile, in a CD/DVD compatible device, it is not impossible to readout the information on the signal surface 102 of the CD 100 by the laserlight having a wavelength not larger than 650 nm. It is also notimpossible to focus the laser spot at a separation approximately 1.2 mmfrom the disc surface 105 of the CD 100. It is however best to use anoptical pickup device having its various characteristics optimized forthe CD 100 in view of playback characteristics.

The CD-R 1 10 also has an organic dye layer 114 which has an absorptiondependence on a wavelength, such that, if the laser light having awavelength not larger than 650 nm is used, data cannot be reproducedcorrectly. That is, with the CD-R 110, light absorption of theilluminated laser light of not larger than 650 nm by the organic dyelayer 114 is increased to lower the reflectivity. In addition, themodulation factor of the laser light by the pits on the signal surface112 is lowered. When recording data, pits are formed with absorption andreflectance properties suited to laser light of wavelength of 780 nm, itis not possible to obtain a sufficient modulation factor even ifattempts are made to read out the pits using laser light of otherwavelengths.

It is thus desirable to use at least an objective lens and a laser lightsource dedicated for each optical disc type in case of an optical discdevice which is compatible for the CD 100 (CD-R 110) and the DVD 120.

Thus, the optical disc device of the invention, as now explained, has anoptical pickup la, dedicated to the CD 100 and the CD-R 110, and adifferent optical pickup 1 b dedicated to the DVD 120. The CD 100, CDR110 and the DVD120 are collectively termed an optical disc D.

FIG. 2 shows a perspective view of a playback driving portion (aso-called mechanical deck portion) of the optical disc in the opticaldisc device.

This mechanical deck includes, on a main body portion of a sub-chassis11, a variety of units required for reproducing data from an opticaldisc. The loaded optical disc D is mounted on a turntable 7 which isdriven by a spindle motor 6 for rotating the optical disc.

The optical pickup 1, illuminating the laser light on the rotatingoptical disc for extracting information from the reflected light,includes, within its shell, a CD pickup 1 a, having an optical systemand a laser light source, optimized for the CD 100 (CD-R 110), and a DVDpickup 1 b, having an optical system and a laser light source, optimizedfor the DVD. These pickups 1 a, 1 b are provided independently of eachother. A laser output end of the CD pickup la is an objective lens 2 afor use with a CD, while a laser output end of the DVD pickup 1 b is anobjective lens for use with a DVD 2 b.

The optical pickup 1 is slidable along the disc radius by a so-calledsled mechanism. To this end, a main shaft 8 a and a sub-shaft 12 areprovided on both sides of the optical pickup 1. The main shaft 8 a ispassed through a holder 8 g of the optical pickup 1, while the sub-shaft12 is passed through an opposite side holder portion, not shown, so thatthe optical pickup 1 is movable along the shaft length as the opticalpickup 1 is supported by the main shaft 8 a and the sub-shaft 12.

As a mechanism for moving the optical pickup 1, a sled motor 8 b, andsled transmitting gears 8 c, 8 d and 8 e are provided, while a rack gear8 f is mounted in the vicinity of the holder portion 8 g of the opticalpickup 1.

When the sled motor 8 b is run in rotation, its rotational power istransmitted to the sled transmitting gears 8 c, 8 d, 8 e in this order.Since the thread transmitting gear 8 e meshes with the rack gear 8 f,the transmitted rotational power causes the optical pickup 1 to be movedalong the shaft. Thus, the optical pickup 1 is moved towards the innerand outer disc rim portions by rotation of the sled motor 8 b in theforward and reverse directions.

FIG. 3 is a block diagram showing essential portions of the optical discdriving device.

The optical disc D is loaded on the turntable 7, also shown in FIG. 2,and is rotated by the spindle motor 6 at CLV or CAV during playbackoperation.

By the optical pickup 1, data recorded as pits on the optical disc D areread out. In actuality, two independent optical pickups, that is the CDpickup 1 a and the DVD pickup 1 b, are provided as the optical pickup 1,as discussed previously.

The CD pickup 1 a is provided with an optical system suited to the CD100 and the CD-R 110. A laser diode 4 a, operating as a laser lightsource, has a center output wavelength of 780 mn, with the objectivelens 2 a for use with a CD having NA=0.45. The objective lens 2 a foruse with a CD is held by a biaxial mechanism 3 a for movement in thetracking direction and in the focussing direction.

The optical pickup for DVD 1 b has an optical system optimum for the DVD120. A laser diode 4 b, operating as a laser light source, has a centeroutput wavelength of 650 nm or 635 nm, with the objective lens 2 b foruse with a DVD having NA=0.6. The objective lens 2 b for use with a DVDis held by a biaxial mechanism 3 b for movement in the trackingdirection and in the focussing direction.

If the optical disc D is the CD 100, the playback operation is performedby the pickup 1 a for use with a CD. The reflected light informationfrom the optical disc D is detected by a photodetector 5 a and convertedinto electrical signals corresponding to the amount of received light soas to be supplied to a RF block 21.

If the optical disc D is the DVD 120, the playback operation isperformed by the pickup for DVD 1 b. In this case, the reflected lightinformation from the optical disc D is detected by a photodetector 5 band converted into electrical signals corresponding to the amount ofreceived light so as to be supplied to the RF block 21.

The CD pickup 1 a and the DVD pickup 1 b are provided respectively, withphotodetectors 5 a , 5 b, each being an eight-segment photodetector,made up of four-segment detectors S_(A), S_(B), S_(C) and S_(D), oneither sides of which two-segment detectors S_(E), S_(F) and two-segmentdetectors S_(G), S_(H) are provided, as shown in FIG. 4.

The RF block 21 includes a current-voltage conversion circuit, anamplifier circuit and a matrix calculation circuit and generatesnecessary signals based on signals from the photodetectors 5 a , 5 b.The RF block 21 generates RF signals as playback signals, e.g.,focussing error signals FE and tracking servo signals TE for servocontrol, pull-in signals PI, as so-called sum signals, and discdiscrimination signals DD_(PI), DD_(AND) and DD_(A/D).

From detection signals A, B, C and D of the detectors S_(A), S_(B) S_(C)and S_(D) of the eight-segment photodetector, the RF block 21 generatesthe focussing error signals FE and the pull-in signal PI by thefollowing equations:

FE=(A+C)−(B+D)

PI=A+C+B+D

For generating tracking error signals TE, the RF block 21 has a trackingblock 40 configured as shown in FIG. 5.

The tracking block is a block for generating tracking error signals TEfrom the detection signals A to H of the eight-segment photodetector,and has three tracking error signal generating blocks 41, 42 and 43 forgenerating three tracking error signals 3SP, DPP and DPD, respectively,as shown in FIG. 5. The tracking block selects between the threetracking error signals 3SP, DPP or DPD using a changeover switch 44 tooutput the selected signal via an output unit 45. The changeover switch44 is a four-input switch and is adapted for selecting an external inputsignal AUX. The changeover switch 44 is switching-controlled, dependingon the type of the optical disc D, by the above-mentioned systemcontroller 30 adapted for discriminating the type of the optical disc Dbased on the disc discrimination signals DD_(PI), DD_(AND) and DD_(A/D),as shown in FIG. 3.

Specifically, the system controller 30 discriminates between the CD 100(CD-R 110) and the DVD 120, having different disc substrate thicknesses,based on the disc discrimination signal DD_(PI), while discriminatingbetween the DVD 120 and a DVD-RW 130, as later explained, by differentreflectivities, based on the disc discrimination signal DD_(A/D). If, asa result of discrimination, the optical disc D loaded on the turntable 7is the CD 100 or the CD-R 110., the system controller 30 switch-controlsthe changeover switch 44 such as to output tracking error signals 3SP.If the disc D is the DVD 120, the system controller 30 switch-controlsthe changeover switch 44 such as to output tracking error signals DPD,whereas, if the disc D is the DVD-RW 130, the system controller 30switch-controls the changeover switch 44 such as to output trackingerror signals DPP.

In the tracking block 40, the first tracking error signal generatingblock 41 generates three-spot type tracking error signals 3SP inaccordance with the equation:

 3SP=(E+F)−(G+H)

That is, the first tracking error signal generating block 41 generates adifference signal between a sum signal of detection signals E and F ofdetectors S_(E) and S_(F) and a sum signal of detection signals G and Hof detectors S_(G) and S_(H). The detectors S_(E) and S_(F) and thedetectors S_(G) and S_(H) are arranged on either side of the detectorsS_(A) to S_(D), arranged at the center of the eight-segmentphotodetector 5 a, 5 b, as discussed previously.

The present system is a generic detection system for detecting atracking error during reproduction of a laser beam spot for therecording track generated on the signal surface of the optical dischaving a thickness of approximately 1.2 mm, that is the CD 100 or theCD-R 110.

On the other hand, the second tracking error signal generating block 42generates tracking error signals DPP of the differential push-pullsystem in accordance with the equation:

DPP={(A+D)−(B+C)}−{(F+H)−(E+G)}

The present system is a detection system used for recording/reproducingan optical disc DVD-RW (Rewritable) which is a rewritable recordingmedium, now being researched, pursuant to the DVD standard. The physicalstructure of the DVD-RW 130 is hereinafter explained with reference toFIGS. 6a and 6 b.

Similarly to the DVD 120, the DVD-RW 130 has a signal surface formed ata spacing of approximately 0.6 mm from the disc surface. In a recordablearea of the instant embodiment of the DVD-RW 130 is pre-formed atracking pre-groove 132 extending spirally from the inner rim to theouter rim, as shown in FIG. 6a.

This pre-groove 132 is formed on a disc substrate 131, and has its leftand right sidewall portions meandering at a pre-set period in meetingwith address information, as shown in FIG. 6b showing part of thepre-groove to an enlarged scale. That is, the pre-groove 132 ismeandering at a pre-set period corresponding to wobbling signalsgenerated on the basis of the addresses. The area confined betweenneighboring pre-grooves 132, is a land 133. The surface of the discsubstrate 131 formed with the pre-groove 132 and the land 133 is coatedwith a phase-transition recording film, as a recording layer, having itsreflectivity changed depending on the crystallized state. Data arerecorded on the pre-groove 132 as the recording track.

In recording/reproducing the data on or from the DVD-RW 130, the DVDpickup 1 b generates three light beams by a diffraction lattice andarrays both side beam spots on the recording surface of the optical discwith an offset of one-half the track pitch along the disc radiusrelative to the mean beam spot. The reflected light of the main beam isdetected by the split detectors S_(A), S_(B), S_(C) and S_(D) of theeight-segment photodetector 5 a, 5 b shown in FIG. 4 so as to be outputas detection signals A to D. On the other hand, the reflected light ofthe side beams is detected by the split detectors S_(E), S_(F) and thesplit detectors S_(G) and S_(H) so as to be output as detection signalsE to H. The above-mentioned calculations are executed on the detectionsignals A to H detected by the detectors S_(A) to S_(H) for producingthe tracking error signals DPP of the differential push-pull system. Thetracking error signals DPP are freed of offset components applied byobjective lens movement on tracking error signals of the conventionalpush-pull system.

In addition, the third tracking error signal generating block 43 isconfigured as shown in FIG. 7 for generating the tracking error signalDPD of the differential phase detection (DPD) system from the detectionsignals A, B, C and D of the detection signals A to H of theeight-segment photodetector, 5 a, 5 b.

The present system is a tracking error detection system for an opticaldisc, such as an optical disc having a thickness of approximately 0.6mm, and being higher in recording density than the CD 100.

That is, the third tracking error signal generating block 43 includesDPD filters 46A, 46B, 46C and 46D, supplied with detection signals A toD of the detection signals A to H of the eight-segment photodetector 5a, 5 b detected by the four central detectors S_(A), S_(B), S_(C) andS_(D) of the photodetector 5 a, 5 b detecting the reflected light of themain beam, and level comparators 47A, 47B, 47C and 47D supplied with thedetection signals A to D bandwidth-limited by the DPD filters 46A to46D, respectively. The third tracking error signal generating block 43also includes phase comparators 48A, 48B supplied with output signals ofthe level comparators 47A, 47B, 47C and 47D and an integration circuit49 supplied with output signals of the phase comparators 48A, 48B.

In the third tracking error signal generating block 43, the levelcomparators 47A, 47B, 47C and 47D compare the detection signals A to D,entered via DPD filters 46A, 46B, 46C and 46D, to a pre-set level VC,for converting the detection signals A to D to binary-valued signals.The phase comparators 48A, 48B phaseompare the binary-valued detectionsignals A to D. The maximum operating frequency of the phase comparators48A, 48B is 10 MHZ, as illustrated at FIG. 9. The integrating circuit 49integrates the output signals of the phase comparators 48A, 48B with 30kHz for outputting the tracking error signals DPD.

The DPD filters 46A, 46B, 46C and 46D of input units of the thirdtracking error signal generating block 43 are each made up of ahigh-pass filter HPFI for cutting dc components, two band-pass filtersBPFI, BPF2 for amplifying EFM+signal components and an output selectionswitch SWDPD for selecting between the band-pass filters BPFI, BPF2. Thefrequency response can be changed over by selecting one of the twoband-pass filters BPFI, BPF2 by the output selection switch SWDPD, asshown in FIG. 8.

The output selection switch SW_(DPD) is switch-controlled, depending onthe type of optical disc 30, by the above system controller 30 whichdiscriminates the type of optical disc D based on the above discdiscrimination signals DD_(PI), DD_(AND) and DD_(A/D), shown in FIG. 3.

That is, the system controller 30 discriminates between the CD 100 andthe DVD 120, by the disc discrimination signals DD_(PI), as laterexplained, and changes over the output selection switch SWDPD forselecting the band-pass filter BPF2 having a passband on a higher sidethan the band-pass filter SPFI if the disc is the DVD 120.

The RF block 21 generates a mirror signal MIRR by a mirror block 50configured as shown in FIG. 10.

This mirror block 50 includes a low-pass filter 51, provided at an inputunit supplied with a RF signal RF_AC, obtained as a detection signalfrom the photodetectors 5 a, 5 b, and an amplifier circuit 52 suppliedwith an output signal LPF_(OUT) of the low-pass filter 51. The mirrorblock 50 also includes a peak-holding circuit 53 and a bottom-holdingcircuit 54, supplied with an output signal AMP_(OUT) of the amplifiercircuit 52. The mirror block 50 also includes a reference level signalgenerating circuit 55 supplied with output signals PKH_(OUT) andBMH_(OUT) of the peak-holding circuit 53 and the bottom-holding circuit54. The mirror block 50 further includes a level comparator circuit 56supplied with a reference level signal REF from the reference levelsignal generating circuit 55, and the output signal AMP_(OUT) of theamplifier circuit 52.

In this mirror block 50, the low-pass filter 51 is used for extracting atraversing signal from the RF_AC shown in FIG. 11A and has its cut-offfrequency changed over between 60 kHz and 30 kHz by a switch SW_(LPF)which is switch-controlled by the system controller 30 depending on thetype of the optical disc D.

That is, the system controller 30 discriminates the type of the opticaldisc D, by the method as later explained, based on the discdiscrimination signals DD_(PI), for changing over the switch SWLPF to 60kHz or to 30 kHz for the DVD 120 and for the CD 100, respectively.

On the other hand, the amplifier circuit 52 is used for amplifying theoutput signal LPF_(OUT) of the low-pass filter 51, that is thetraversing signal, and has its gain changed over between 12 dB and 2 dBby the switch SW_(AMP), which is switch-controlled by the systemcontroller 30 depending on the type of the optical disc D.

This switching is done, for coping with recently developed rewritableoptical discs CD-RW or DVD-RW, employing a phase transition recordingfilm. Specifically, the reflectivity of the optical disc is detected bythe disc discrimination signals DD_(A/D) and the switch SW_(AMP) ischanged over to raise the gain to 12 dB for reproducing data from thedisc having a reflectivity of ¼ to ⅕ of the reflectivity of the CD 100.

Further, the peak-holding circuit 53 holds the peak level of the outputsignal AMP_(OUT) of the amplifier circuit 52 and feeds the output signalPKH_(OUT) to the reference level signal generating circuit 55. Also, thebottom-holding circuit 54 holds the bottom level of the output signalAMP_(OUT) and feeds the output signal BMH_(OUT) to the circuit 55. Thepeak-holding circuit 53 and the bottom-holding circuit 54 are configuredfor setting the time constants in 32 steps by the system controller 30responsive to the spindle speed or the traversing speed.

On the other hand, the reference level signal generating circuit 55generates a reference signal REF, having a signal level intermediatebetween the output signals PKH_(OUT) of the peak-holding circuit 53 andBMH_(OUT) of the bottom-holding circuit 54, from these output signalsPKH_(OUT) and BMH_(OUT), in accordance with the equation:

REF=(PKH_(OUT)+BMH_(OUT))/2.

The level comparator circuit 56 compares the output signal AMP_(OUT) ofthe amplifier circuit 52, that is the amplified traversing signal, tothe reference level signal REF from the reference level signalgenerating circuit 55, as to the signal level, and generates a mirrorsignal MIRR shown in FIG. 11D.

Also, the RF block 21 generates disc discrimination signals DD_(PI),DD_(AND) and DD_(A/D) by a discrimination signal generating block 60configured as shown in FIG. 12.

This discrimination signal generating block 60 includesconvert-to-binary circuits 61, 62 for converting the focussing errorsignal FE=(A+C)+(B+D) and the pull-in signal PI=A+C+B+D, generated fromthe detection signals A, B, C and D by the detectors S_(A) to S_(D) Ofthe eight-segment photodetector, into binary signals. The discriminationsignal generating block 60 also includes an AND gate 63 for finding thelogical product of output signals DD_(FE) and DD_(PI) of theconvert-to-binary circuits 61, 62 and an A/D converter 64 for convertingthe signal level of the pull-in signal PI into digital data. The outputsignal DD_(PI) of the convert-to-binary circuit 62, the logical productsignal DD_(AND) from the AND gate 63 and the output signal DD_(A/D) ofthe A/D converter 64 are routed as disc discrimination signals to thesystem controller 30.

Referring back to FIG. 3, signals generated by the RF block 21 arerouted to a convert-to-binary circuit 25, a servo processor 31 and tothe system controller 30 through a discrimination signal generatingcircuit 60 of the RF block 21. That is, the playback RF signals from theRF block 21 are routed to the convert-to-binary circuit 25, while thefocussing error signals FE, tracking error signals TE and the pull-insignals PI are routed to the servo processor 31, and the discdiscrimination signals DD_(PI), DD_(AND) and DD_(A/D) are routed to thesystem controller 30.

The playback RF signals, obtained by the RF block 21, are processed bythe convert-to-binary circuit 25 for conversion to so-calledeight-to-fourteen modulation signals (EFM signals) in case of the CD orto EFM+signals in case of the DVD. The converted signals are routed to adecoder 26. The decoder 26 executes EFM demodulation or CIRC decodingand, if need be, CD-ROM decoding or MPEG decoding for the informationread out from the optical disc D.

The servo processor 31 generates various servo signals, such asfocussing, tracking, sled or spindle servo drive signals, from thefocussing error signals FE and tracking error signals TE from the RFblock 21, and from spindle error signals SPE from the system controller30 for executing the servo operations.

That is, the focussing drive signals or tracking drive signals aregenerated, responsive to the focussing error signals FE and trackingerror signals TE, so as to be output at the switch 24. If the opticaldisc D is the CD 100 or DVD 120, a terminal TCD or a terminal TDV of theswitch 24 is selected, respectively.

During reproduction of the CD 100, the focussing drive signals and thetracking drive signals generated responsive to the focussing errorsignals FE and the tracking error signals TE, respectively, from the RFblock 21 are routed to a biaxial driver 18 a which then drives thebiaxial mechanism 3 a of the CD pickup 1 a. This completes a trackingservo loop and the focussing servo loop by the CD pickup 1 a, RF block21, servo processor 31 and the biaxial driver 18 a.

During reproduction of the DVD 120, the focussing drive signals and thetracking drive signals generated responsive to the focussing errorsignals FE and the tracking error signals TE from the RF block 21 by theservo processor 31 are routed to a biaxial driver 18 b which then drivesthe biaxial mechanism 3 b of the DVD pickup 1 b. This completes afocussing servo loop and a tracking servo loop by the DVD pickup 1 b, RFblock 21, servo processor 31 and the biaxial driver 18 b.

The servo processor 31 routes to a spindle motor driver 19 a spindledrive signal generated responsive to a spindle error signal SPE. Thespindle motor driver 19 is responsive to the spindle drive signal toapply a three-phase drive signal to the spindle motor 6 to cause the CLVrotation of the spindle motor 6. The servo processor 31 is responsive tothe spindle kick/brake control signals from the system controller 30 tostart or stop the spindle motor 6 by the spindle motor driver 19.

The servo processor 31 generates a sled drive signal, based on the slederror signal produced from the tracking error signals TE or accessingexecution control from the system controller 30 for supplying thegenerated sled drive signal to a sled driver 17. The sled driver 17 isresponsive to the accessing execution control to drive a sled mechanism8. This sled mechanism 8 is made up of the main shaft 8 a, sled motor 8b and the sled transmission gears 8 c, 8 d and 8 e, shown in FIG. 2,such that optimum sliding movement of the optical pickup 1 occurs by thethread driver 17 driving the sled motor 8 b responsive to the sled drivesignal.

A laser diode 4 a in the CD pickup 1 a is driven by laser driver 20 a.On the other hand, a laser diode 4 b in the DVD pickup 1 b is driven bylaser driver 20 b.

The laser drivers 20 a, 20 b each have enclosed therein an automaticpower control circuit (APC) (see FIG. 13) for controlling the laseroutputs of the laser diodes 4 a, 4 b so that a detection output of afront monitor photodiode PD adapted for detecting the amount of laserlight radiated from the laser diodes 4 a, 4 b will be constant. The APCcircuit is made up of, for example, three stages of amplifier circuits71, 72 and 73, as shown in FIG. 13. The APC circuit operates foramplifing a detection output of the front monitor photodiode PD by thefirst-stage amplifier circuit 71 and the next-stage amplifier circuit 72for feeding back the amplified output to the output stage amplifiercircuit 73 driving the laser diode LD for driving-control of the laserdiode LD so that the detection output of the front monitor photodiode PDwill be constant. The APC circuit of FIG. 13 has, in its initial-stageamplifier circuit 71, a gain-switching switch SW_(APC) which is adaptedfor switching/setting the closed loop gain of the APC circuit between33.2 dB and 28.8 dB as shown in FIG. 14. The switch SW_(APC) isswitch-controlled by the system controller 30 depending on the type ofthe optical disc D.

Specifically, the system controller 30 of FIG. 3 discriminates, based onthe disc discrimination signals DD_(PI), DD_(AND) or digitized focussingerror signals DD_(FE), as later explained, whether the optical disc D isa single-layer disc or a double-layer disc. If the disc D is adouble-layer disc lower in reflectivity than tesingle layer disc, thesystem controller 30 causes the changeover switch SW_(APC) shown in FIG.13 to be changed over so that the closed-loop gain of the APC circuitwill be equal to 28.8 dB. This increases put of the laser diode 4 b.Conversely, the single-layer disc is higher in reflectivity than thedouble-layer disc, such that the system controller 30 causes thechangeover switch SW_(APC) to be changed over so that closed-loop gainof the APC circuit will be equal to 33.2 dB to lower the output of thelaser diode 4 b.

If, in the case of the double layer disc, the modulated data(eight-to-sixteen modulated signal) is demodulated by the decoder 26 ofFIG. 3, the system controller 30 judges, based on the discriminatingsignal recorded on the signal surface of each signal recording layer,whether data being reproduced is data recorded on the first signalsurface 122 or that receded on the second signal surface 123 as shown inFIG. 1c. The second signal surface 124, that is the signal surfaceseparated from the disc surface 128, has a reflectivity lower than thatof the first signal surface 122 because the laser light is illuminatedon the second signal surface 124 via the first signal surface 122. Thus,if the playback signal surface is the second signal surface 124, thesystem controller 30 lowers the closed-loop gain to a value lower thanthat for the first signal surface 122, while raising the output of thelaser diode 4 b. Thus, gain control adapted to each signal recordinglayer leads to further stabilized signal reproduction.

The servo processor 31 generates a laser driving signal for effectuatinglaser light emission of the optical pickup 1 during reproduction underinstructions from the, system controller 30 to route the generated laserdriving signal to the switch 23 as shown in FIG. 3. The switch 23 hasits terminal TCD and its terminal TDV selected if the optical disc D isthe CD 100 or the DVD 120, respectively. Thus, the laser diode 4 a or 4b emits light depending on the type of the optical disc D to bereproduced.

The above-described servo or decoding operations are controlled by thesystem controller 30 comprised of, for example, a micro-computer.

The start or termination operations of reproduction track accessing,fast feed reproduction or rewind reproduction can be realized by controlof the operation of the servo processor 31 or the optical pickup 1 bythe system controller 30.

This optical disc device can cope with both the CD 100 and the DVD 120,using either the optical pickup 1 a or 1 b, RF block 21, laser driver 20a, 20 b and the biaxial driver 18 a or 18 b are provided for devoted usewith the CD 100 or the DVD 120, respectively. Thus, for properlyexploiting these devoted circuit systems, it is judged whether theoptical disc D is the CD 100 or the DVD 120, when the optical disc isloaded in position, for setting to one of the terminals TCD or TDV ofeach of the switches 23 and 24 under control by the system controller30.

Among the optical discs D handled by the present optical disc device,the CD 100 and the CD-R 110 have the signal surfaces 102 and 112 at aseparation of approximately 1.2 mm from the disc surfaces 105 and 116,respectively. On the other hand, the DVD 120 has the signal surface 122at a separation of approximately 0.6 mm from the disc surface 128.

For explanation sake, the CD 100 and the CD-R 110 are each termed a 1.2mm single-plate disc, while the DVD 120 is termed a 0.6 mm laminateddisc.

The objective lens 2 a of the CD pickup la is moved, by focussing servooperation, in a direction towards or away from the CD 100 so that thelaser light will be focussed on the signal surface 102 of the CD 100(1.2 mm single-plate disc) as shown in FIG. 15c.

If focussing servo control is executed directly after loading of theoptical disc D, such as the CD 100 or the DVD 120, the objective lens 2a first is compulsorily moved within the focussing search range fordetecting focussing pull-in range corresponding to the linear area of aS-shaped curve. If the focussing servo loop is turned on with theobjective lens 2 a in the focussing pull-in range, the focussing servocontrol is subsequently executed for convergence to the just-focusstate.

These focussing search and focussing servo operations hold for a DVDoptical pickup 1 b associated with the DVD 120.

It should be noted that the just-focus point is a point of focussing ofthe laser light on the signal surface 122 of the DVD 120, which is the0.6 mm-laminated disc, as shown in FIG. 1c, and differs from the CD 100due to its position along the disc thickness. For both the objectivelens 2 a for use with a CD and the objective lens 2 b for use with aDVD, the focussing search range is from the bottom position of FIGS. 15aand 16 a as far as the top position of FIGS. 15d and 16 d. If theposition of the just-focus state of FIGS. 15c and 16 c is the initialreference position, the focussing search range is ±0.9 mm.

If the objective lens 2 (objective lens 2 a for CD and objective lens 2b for DVD) can be varied in its position state relative to the CD 100 orthe DVD 120, as shown in FIGS. 15a to 15 d or FIGS. 16a to 16 d, thefocussing error signals FE or the pull-in signals PI associated with therespective positions can be obtained as reflected light information datafrom the optical disc D.

In the vicinity of the just-focus point as shown in FIGS. 15c and 16 c,the reflected light is detected at an optimum level, a S-shaped curve isobserved as the focussing error signals FE, while the amplitude level isincreased for the pull-in signal PI. In an assumed state of FIGS. 15b or16 b in which light is focussed on the disc surfaces 105, 128, reflectedlight is detected on the disc surfaces 105, 128, albeit at a lowreflectivity. Thus, a small S-curve is observed as the focussing errorsignals FE, while a small amplitude level is observed as the pull-insignal PI.

Thus, the system controller 30 discriminates the type of the disc D forsetting a parameter suited to the type of the optical disc D, based onthe disc discrimination signals DD_(AND) (see FIG. 12), obtained by anAND gate 63 finding the logical product of output signals DD_(FE) andDD_(PI) of the convert-to-binary circuits 61, 62, output signal DD_(PI)of the convert-to-binary circuits 62 and the disc discrimination signalsDD_(A/D) corresponding to the digitized signal level of the pull-insignal PI by the A/D converter 64. The convert-to-binary circuits 61 and62 convert the focussing error signals FE=(A+C)−(B+D) and the pull-insignal PI=A+C+B+D, generated from the detection signals A, B, C and D bythe detectors S_(A), S_(B), S_(C) and S_(D) of the eight-segmentphotodetector into binary-valued signals.

For example, as the objective lens 2 is compulsorily moved such as in afocussing search, the timing of peak reflection light amplitudedetection due to light reflection from the signal surface of the opticaldisc D with the pull-in signal PI and the timing of peak reflectionlight amplitude detection from reflection from the disc surface 102 or122 are compared to each other, and the time between detection of thetwo amplitudes is measured for discriminating whether the optical disc Dis a CD 100 or a DVD 120. That is, since the separation from the discsurface 105 to the disc surface 102 of the 1.2 mm single-plate disc isapproximately 1.2 mm, and the separation from the disc surface 128 tothe disc surface 122 of the 0.6 mm laminated disc is approximately 0.6mm, the time lag between the timing of just-focussing on the discsurface 105, 128 and detecting a peak amplitude and the timing ofjust-focussing on the signal surface 102, 122 and detecting a secondpeak amplitude differs between the 1.2 mm single-plate disc and the 0.6mm laminated disc. This can be utilized for disc discrimination from,for example, the pull-in signal, as discussed in U.S. patent applicationSer. No. 08/915877 (filed on Aug. 21, 1997).

Similar discrimination can be made using the focussing error signals FE.In the present instance, the following disc discrimination operation isperformed, using the binary-valued disc discrimination signals DD_(PI)converted from the pull-in signal PI by the above-mentionedconvert-to-binary circuits 62.

The system controller 30 commands the servo processor 31 to effect thedriving of the objective lens 2 a, 2 b similar to that for focussingsearch. The servo processor 31 is responsive thereto to route to thebiaxial drivers 18 a, 18 b a signal shown in FIG. 17a as a focussingsearch driving signal.

In the present instance, each switch 22, 24 has its terminal T_(DV)connected in circuit such that the operation for disc discriminationoccurs using the DVD pickup 1 b. To this end, the biaxial driver 18 bdrives the biaxial driver 3 b by the focussing search drive signal asshown in FIG. 17a for compulsorily raising/lowering the objective lensfor DVD 2 b.

In FIGS. 17A-17E, the objective lens 2 b being lowered means such astate in which the objective lens 2 b for use with a DVD is moved in adirection away from the optical disc D, while the objective lens 2 bbeing raised means such a state in which the objective lens 2 b for usewith a DVD is moved in a direction approaching to the optical disc D.Although disc discrimination is possible with the objective lens 2 bbeing raised or with the objective lens 2 b being lowered, it is assumedin the following explanation that disc discrimination is made from asignal derived when the objective lens 2 b is being raised.

If the objective lens 2 a, 2 b is moved within the focussing searchrange, peak signal amplitudes of the pull-in signal PI are observed at atiming when the objective lens 2 a, 2 b reaches the disc surface 105,128 just focus position shown in FIGS. 15b and 16 b and at a timing whenthe objective lens 2 a, 2 b reaches the signal surface 105, 122 justfocus position shown in FIGS. 15c and 16 c.

If the disc loaded is the 1.2 mm single-plate disc having a separationof approximately 1.2 mm between the disc surface 105 and the signalsurface 102, and the objective lens 2 a is raised by the focussingsearch drive signal shown in FIG. 17a, a small signal amplitude is firstobserved at a timing of focussing on the disc surface 105, as shown inFIG. 17b, while a larger signal amplitude is observed at a timing offocussing on the signal surface 102. This pull-in signal is compared toa threshold value TH1 by a comparator circuit 29 for generating adiscrimination signal DD as shown in FIG. 17c. This discriminatingsignal DD is routed to the system controller 30. The system controller30 measures the time between the pulse of the discriminating signal DDobtained at a timing associated with just focussing at the disc surface105 and the pulse of the discriminating signal DD obtained at a timingassociated with the just focussing at signal surface 102. This measuredtime is denoted as t1.

If the disc loaded is the 0.6 mm double-plate disc having a separationof approximately 0.6 mm between the disc surface 128 and the signalsurface 122, and the objective lens 2 b is raised by the focussingsearch drive signal shown in FIG. 17a, a small signal amplitude is firstobserved at a timing of focussing on the disc surface 128, as shown inFIG. 17a, while a larger signal amplitude is observed at a timing offocussing on the signal surface 122. Thus, a discriminating signalDD_(PI),shown in FIG. 17e is routed to the system controller 30. Thesystem controller 30 measures the time between the pulse of thediscriminating signal DD_(PI) obtained at a timing associated with thedisc surface 128 and the pulse of the discriminating signal DD_(PI)obtained at a timing associated with the signal surface 122. Thismeasured time is denoted as t2.

That is, the different measured values t1 and t2 are obtained as tx forthe 1.2 mm single-plate disc and for the 0.6 mm laminated disc, due tothe difference between the just focussing at the disc surface 128, 105and the signal surface 122, 102. Thus, if the system controller 30 holdsan intermediate time tTH between measured values t1 and t2, as referencevalue, it can be judged whether the measured time tx is t1 or t2 in FIG.17, by comparing the measured time tx to the time tTH. That is, it canbe judged whether the optical disc loaded is the CD 100 or the DVD 120.

Meanwhile, similar discrimination can be made with the objective lensbeing lowered. The reason is that the time difference between the twopulses of the disc discrimination signals DD_(PI) is 0 in FIGS. 17c ort4 in FIG. 17e depending on whether the disc D is the CD 100 or the DVD120. However, with the focussing search driving signal, shown in FIG.17a, the objective lens is lowered at a higher speed than when it israised, such that the measured time values 0 and t4 between the twopulses of the discriminating signal DD_(PI), are shorter time valuesthan the measured time between time values t1 and t2. Thus, in theinstance of FIG. 17, it is more meritorious for accurate discriminationto make discrimination with the objective lens being raised, althoughthe clock frequency for counting the measured time needs to be takeninto account. Such relative merit or demerit may, of course, beeliminated if the objective lens raising speed is set so as to be equalto the objective lens lowering speed. If the lowering speed is slower,it is more meritorious to make discrimination with the lens 2 a, 2 bbeing lowered.

The processing by the system controller 30 in this case is hereinafterexplained.

If it has not been judged whether the optical disc D loaded is the 1.2mm single-plate disc or the 0.6 mm laminated disc, it does not matter,as a principle, which of the CD pickup la and the DVD pickup 1 b is usedfirst.

That is, one of the optical pickups is used for making discdiscrimination in accordance with the system explained with reference toFIGS. 17A-17E. It does not matter which optical pickup 1 a or 1 b isused for effectuating disc discrimination.

It is herein assumed that the DVD pickup 1 b is used. Referring to FIG.18, an illustrative processing of the system controller 30 in which theloaded optical disc D is discriminated as the disc type and subsequentlyreproduced is explained with reference to FIG. 18.

FIG. 18 shows a processing step in which the power source is turned on.If the power source is turned on, and various parmeters are set, by wayof initializing operations, the system controller 30 waits for insertionof the optical disc D, as a first step F101.

If optical disc D is inserted, processing transfers to step F102 to setthe DVD pickup mode for employing the DVD pickup 1 b.

The DVD pickup mode is a mode in which each switch 23, 24 has itsterminal T_(DV) connected in circuit. The system controller 30 thenproceeds to step F103 to proceed with disc type discrimination.

In this disc type discrimination, the DVD pickup 1 b is used, becausethe DVD pickup mode is set at step F102.

For disc type discrimination, the DVD objective lens 1 b is compulsorilyraised or lowered within the focussing search range. This objective lensdriving is started at step F103. That is, the start of outputting thefocussing search drive signal such as shown in FIG. 17a is commanded. Ofcourse, laser output of the laser diode 4 b is also started at thistime.

The system controller 30, managing control for raising or lowering theDVD objective lens 1 b within the focussing search range, detects thedisc discrimination signals DD supplied from the discrimination signalgenerating circuit 60, at step F104, for measuring the time periodbetween two pulses shown in FIGS. 17c and 17 e.

There are occasions wherein, due for example to too low of a reflectionlevel from a disc surface, two pulses as the disc discrimination signalsDD are not correctly observed during raising or lowering of the DVDpickup 1 b. In such case, a measurement error is deemed to have occurredat step F105 such that processing reverts to step F103 to effectuateagain the objective lens driving and measurement. In actuality,limitations are preferably placed on the number of times re-trialoperations are performed on occurrence of measurement errors withoutallowing retrial operations to be performed an arbitrary number oftimes.

After measuring the time period between two pulses of the discriminatingsignal DD_(PI), the measured time value is compared at step F106 to thetime tTH as the reference value. If, as a result of the comparison, themeasured value is longer, it is judged at step F108 that the opticaldisc D is the 1.2 mm single-plate disc, that is the CD 100.

Since the DVD pickup 1 b has been used for the discriminating operation,the result of judgment indicates that this state is not in meeting withthe currently loaded optical disc D (CD 100). Thus, the mode is switchedat step F108 to the CD pickup mode. That is, the mode is set in whicheach of the switches 22 to 24 has its terminal T_(CD) connected incircuit and the CD pickup 1 a is in use.

Conversely, if as the result of comparison at step F106, the referencetime tTH is longer, it is judged at step F107 that the optical disc D isthe 0.6 mm laminated disc, that is the DVD 120.

If the disc D is judged to be the DVD 120, the pickup mode state is notchanged, because the DVD pickup mode has already been set.

If the pickup mode setting in meeting with the disc discrimination andthe results of disc discrimination has come to a close, processingtransfers to actual playback operation. That is, focussing search isstarted at step F109 to start the focussing search to pull-in thefocussing servo. After the pull-in of the focussing servo has beenterminated, processing transfers to step F110 and step F111 to carry outother starting operations. That is, processing of the servo system, suchas adjusting the rotation of the spindle motor 6 and turning on of thetracking servo, is completed, while the readout of the optical disc D isenabled. In addition, the necessary management information recorded onthe optical disc D such as TOC, is read. After completion of theseprocessing operations, processing transfers to step F112 to reproducedata from the CD 100 or the DVD 120.

Since the signal level of the pull-in signal PI=A+C+B+D is varied basedon reflectivity of the optical disc D, the system controller 30calculates the reflectivity of the optical disc D from the discdiscrimination signals DD_(A/D) at a time point of completion of thefocussing servo pull-in. The system controller 30 switch controls thechangeover switch SW_(APC) of the APC e circuit enclosed in the laserdrivers 20 a, 20 b, depending on the reflectivity of the optical disc D,for switching the closed-loop gain of the APC circuit between thesingle-layer disc and the double-layer disc. This enables laser light ofthe optimum power from the laser diode LD of the optical pickup 1 a, 1 bto the single-layer disc and the double-layer disc, respectively, forstable read out of signals from the optical disc D by the optical pickupI to produce playback RF signals with optimum S/N ratio.

The disc discrimination signals DD_(A/D) can also be used fordiscriminating the optical discs D having different reflectivities dueto differences in the material of the recording layer making up thesignal surface, such as CD and CD-RW or DVD and DVD-RW.

Referring to FIGS. 17A-17E, if the objective lens 2 a, 2 b iscompulsorily moved within the focussing search range by the biaxialdrivers 18 a, 18 b shown in FIG. 3, by way of performing a focussingsearch operation, a sole S-curve is obtained as the focussing errorsignal FE and a pull-in signal PI within the range of the S-curve, asshown in FIGS. 19a and 19 c, respectively, for a single-layer disc,whereas two S-curves are obtained as the focussing error signal FE and apull-in signal PI astride the two s-curves, as shown in FIGS. 20a and 20c, respectively for a double-layered disc. It is noted that thefocussing error signal FE and the pull-in signal PI are generated fromthe detection signals A, B, C and D by the detectors S_(A), S_(B), S_(C)and S_(D) of the eight-segment photodetector by the equationsFE=(A+C)−(B+D) and PI=A+C+B+D, respectively. The focussing error signalFE and the pull-in signal PI are converted by the convert-to-binarycircuits 61, 62 to find the logical product by the AND gate 63. That is,the pull-in signal PI=A+C+B+D, a sum signal of the detection signals Ato D by the above photodetector, is converted to a binary-valued signalat a pre-set level to generate the disc discrimination signals DD_(PI)shown in FIGS. 19d and 20 d as discriminating pulses, the number ofwhich is counted during a gating period supplied by a gate pulse fordiscriminating the types of the optical discs D having different numbersof signal recording layers based on the results of the counting. It isnoted that, in the single-layer disc, the disc discrimination signalDD_(AND) goes high ‘H’ only once by a sole focussing search operation,as shown in FIG. 19e, whereas, in the double-layer disc, the discdiscrimination signal DDANM goes high ‘H’ twice by a sole focussingsearch operation, as shown in FIG. 20e. This discriminating operationenables discrimination of optical discs D with different reflectivitieswhich is more accurate than that using the disc discrimination signalsDDAM representing signal levels of the pull-in signal.

That is, the system controller 30 can discriminate between thesingle-layer disc and the double-layer disc by the disc discriminatingoperation in accordance with the flowchart shown in FIG. 21.

Specifically, if the disc discriminating operation is started, it isjudged at step S1 whether the input, that is the disc discriminationsignals DD_(AND), has gone high ‘H’. If the input is ‘H’, processingtransfers to step S2.

At this second step S2, it is judged whether or not the input, that isthe disc discrimination signal DD_(AND), is low ‘L’. If the input is atlogic ‘L’, processing transfers to step S3.

At this third step S2, it is judged whether or not the input, that isthe discrimination signal DD_(AND), has become logical H. When the inputbecomes logical H, processing transfers to step S4.

At this step S4, it is judged whether or not the input, that is the discdiscrimination signals DD_(AND), again is low ‘L’. If the input islogical ‘L’, processing transfers to step S5 to set parameters ofvarious circuits associated with the double-layer disc.

If the result of decision at step S3 is NO, that is if the input is notagain ‘H’, processing transfers to step S6.

At this sixth step S6, it is judged whether or not the number of timesof repetition of the decision processing at the third step S3 is 100. Ifthe result is NO, that is if N is not equal to 100, processing transfersto step S7 to wait for Ims. At the next step S8, N is set to N=N+1.Then, processing reverts to step S3. The decision processing of thisthird step S3 is repeated. If the result of decision at the sixth stepS6 is YES, that is if N=100, that is if the pulse of the discdiscrimination signals DD_(AND) corresponding to the second layer is notobtained after lapse of 100 ms, processing transfers to step S9 to setparameters of respective circuits associated with the single-layer disc.

In the above-described embodiment, three types of disc discriminationsignals DD_(A/D), DD_(PI) and DD_(AND) are used for discriminating typesof optical discs D. The disc discrimination signal DD_(A/D) is obtainedby converting the signal level of the pull-in signal PI into digitaldata, whereas the disc discrimination signal DD_(PI) is obtained byconverting the pull-in signal PI into a binary-valued signal, and thedisc discrimination signal DD_(AND) is obtained by ANDing thebinary-valued version of the focussing error signal FE with the discdiscrimination signal DD_(PI). Alternatively, the disc discriminationsignal DD_(PI) obtained by converting the pull-in signal PI into abinary valued signal and the disc discrimination signal DD_(FE) obtainedin converting the signal level of the focussing error signal FE intodigital data may also be used for disc discrimination, as shown in theflowcharts of FIGS. 22 and 23. In this case, the focussing error signalFE is directly supplied to an A/D input port of the system controller30.

As an operating example of using the DVD pickup 1 b, an illustrativeprocessing of the system controller 30 in which the type of the loadedoptical disc D is discriminated on power up of the loaded optical discdevice before proceeding to data reproduction is explained withreference to FIGS. 22 to 23 and 24A-24E.

If the power source is turned on, and various parameters are first set,by way of initialization, the system controller 30 at step F201 firstturns the laser diode 4 b on. Then, at step F202, the system controller30 compulsorily lowers the DVD optical pickup 1 b within the focussingsearch range at an optical axis position furthest away from the opticaldisc D. At step F203, the signal level of the focussing error signal FE,with the DVD optical pickup 1 b lying at the position furthest from theoptical disc D, is sampled, with the sampled value being set asreference value (FF₀).

At the next step F204, a focussing search timeout measurement timer isstarted. This focussing search timeout is set for preventing the voltagefrom being continuously applied across the focussing control in case ofnon-detection of the reflected light from a signal surface of theoptical disc D and for preventing the system controller 30 from pollingwithout proceeding to the next processing. The focussing search timeoutis herein set to 800 ms.

At step F205, the search operation of raising the DVD optical pickup 1 bis started.

At step F206, it is judged whether or not the disc discrimination signalDD_(PI), is at logical ‘H’. Since the disc discrimination signal DD_(PI)is a binary-valued version of the pull-in signal PI representing thelight volume of the reflected light by the optical disc D, the logical‘H’ is set for the state of detection of the surface or the reflectedlight from its signal surface, if the optical disc D is loaded inposition.

If the result of judgment at step F206 is NO, that is if the discdiscrimination signal DD_(PI) is not at logical ‘H’, processingtransfers to step F207 to judge whether or not the value of thefocussing search timeout timer has reached 800 ms to reach timeout. Iftimeout has not been reached, processing reverts to step F206 so thatthe decision of the disc discrimination signals DD_(PI), is repeateduntil timeout of the focussing search timeout timer. If the result ofdecision at step F207 is YES, that is if the focussing search timeouttimer has timed out, a decision is given that the optical disc D has notbeen loaded and processing transfers to step F208 to display anindication such as ‘no disc’.

If the result of decision at step F206 is YES, that is if the discdiscrimination signal DD_(PI) is at logic W, a decision is given that anoptical disc D has been loaded in position. Thus, processing transfersto the next step F209 to start a disc discrimination timer and to startcapturing the signal level of the focussing error signal FE. At thisstep F209, it is detected that the disc discrimination signal DD_(PI)has become logical ‘H’ based on the detection of reflected light from asurface of the optical disc D.

At the next step F210, it is judged whether or not the focussing searchtimeout timer has reached 800 ms and timed out. If the timer has nottimed out, processing transfers to step F211 to check whether or not thedisc discrimination signal DD_(PI) is at logical ‘H’. If the result ofdecision at step F210 is YES, that is if the focussing search timeouttimer has timed out, a decision is given that an optical disc D has notbeen loaded. Thus, processing transfers to the above step F208 todisplay an indication such as ‘no disc’.

At step F211, it is judged whether or not the disc discrimination signalDD_(PI) is at logical W. At this step F211, it is detected that the discdiscrimination signal DD_(PI) is at logical ‘H’ by the detection ofreflected light from a signal surface of the optical disc D.

At the next step F212, it is judged whether or not the value of the discdiscrimination timer is smaller than the reference time tTH.Specifically, at this step F212, it is judged whether or not the elapsedtime between detection of the disc discrimination signals DD_(PI) judgedat step F206 when the reflected light from the surface of the opticaldisc D is logical ‘H’ until the disc discrimination signal DD_(PI) isjudged at step F211 by detection of the reflected light from the signalsurface of the optical disc D to be again logical ‘H’ is smaller thanthe reference time tTH. If the result of decision at this step F212 isNO, that is if the value of the disc discrimination timer is longer thanthe reference time tTH, the loaded optical disc D is judged to be a 1.2mm single-plate disc, that is CD 100. Thus, processing transfers to stepF213 to switch to the CD pickup mode of employing the CD pickup 1 a.

If the result of decision at this step F212 is YES, that is if the valueof the disc discrimination timer is shorter than the reference time tTH,the loaded optical disc D is judged to be a 0.6 mm laminated disc, thatis DVD 120. Thus, processing transfers to step F214 to make discdiscrimination of whether the DVD 120 is the single-layered disc or adouble-layered disc in accordance with the flowchart shown in FIG. 23.

If the pickup mode setting corresponding to the disc discrimination andthe results of the disc discrimination have come to a close, the systemcontroller proceeds to actual data reproduction processing.Specifically, the focussing search is started at step F215 for focussingservo pull-in. At step F216, it is judged whether or not focussing servopull-in has been completed. If the result of judgment is YES, processingtransfers to step F217 to perform other starting operations. That is,processing of the servo system such as adjusting the rotation of thespindle motor 6 and turning on of the tracking servo, is completed,while the readout of the optical disc D is enabled. In addition, thenecessary management information recorded on the optical disc D such asTOC, is read. After completion of these processing operations,processing transfers to step F218 to reproduce data from the CD 100, DVD120 or the DVD-RW.

The system controller 30 commands the servo processor 31 to drive theobjective lens 2 b as in the case of the focussing search. The servoprocessor 31 is responsive thereto to supply to the biaxial driver 18 ba signal shown in FIG. 24a as a focussing search drive signal to drivethe biaxial driver 18 b for compulsorily raising the objective lens forDVD 2 b. During the period when the disc discrimination signal DD is atlogical ‘H’ it is judged how many times the S-curve is detected as beingthe focussing error signal FE using the first and second thresholdvalues TH_(—H) and TH_(—L), for discriminating between the single-layerdisc and the double-layer disc.

That is, in the processing for discriminating between the single-layerdisc and the double-layer disc, a focussing error timeout timer is firststarted at the first step S11. This focussing search timeout is set forpreventing the system controller 30 from polling without proceeding tothe next processing in case of failure in detecting the S-curve as thefocussing error signal FE during the logical ‘H’ period of the discdiscrimination signal DD_(PI). The focussing search timeout is hereinset to 40 ms.

At the second step S12, it is judged whether or not the focussing errortimeout timer has timed out. If the focussing error timeout timer hastimed out, it is judged that a detection error has occurred, andprocessing transfers to step S13 to perform error processing. If theresult of decision at the second step S12 is NO, that is if thefocussing error timeout timer has timed out, then processing transfersto a fourth step S14.

At the fourth step S14, the focussing error signal FE is captured via anA/D port to judge whether or not the signal level is larger than thefirst threshold value TH_(—H). If the result of decision at the fourthstep S14 is NO, that is if the signal level of the focussing errorsignal FE is smaller than the first threshold value TH_(—H), processingreverts to the second step S12 to repeat the decision of timeout of thefocussing error timeout timer. If the result of decision at the fourthstep S14 is YES, that is if the signal level of the focussing errorsignal FE is larger than the first threshold value TH_(—H), processingreverts to the fifth step S15.

At the fifth step S15, it is judged whether or not the focussing errortimeout timer has timed out. If the focussing error timeout timer hastimed out, a detection error is judged to have occurred, such thatprocessing transfers to a third step S13 to perform error processing. Ifthe focussing error timeout timer has not timed out, processingtransfers to a sixth step S16.

At this sixth step S16, the focussing error signal FE is captured via anA/D port to judge whether or not the signal level is smaller than thesecond threshold value TH_(—L). If the result of decision at this sixthstep S16 is NO, that is if the signal level of the focussing errorsignal FE is larger than the second threshold value TH_(—L), processingreverts to the fifth step S15 to repeat the decision of timeout of thefocussing error timeout timer. If the result of decision at this sixthstep S16 is YES, that is if the signal level of the focussing errorsignal FE is smaller than the second threshold value TH_(—L), processingreverts to the seventh step S17.

At this seventh step S17, it is judged whether or not the discdiscrimination signal DD_(PI) is at the logical ‘L’. If the result ofjudgment at this step S17 is YES, that is if the disc discriminationsignal DD_(PI) is at the logical ‘L’, it is judged that the disc is thesingle-layer disc in which the S-curve of the focussing error signal FEis detected only once during the logical ‘H’ period of the discdiscrimination signal DD_(PI). Thus, processing transfers to the eighthstep S18 to set parameters of various circuits. If the result ofjudgment at this step S17 is NO, that is if the disc discriminationsignal DD_(PI) is at the logical ‘H’, processing transfers to a ninthstep S19.

At this ninth step S19, it is judged whether or not the focussing errortimeout timer has timed out. If the timer has timed out, it is judgedthat a detection error has occurred, and processing reverts to the thirdstep S13 to perform error processing. If the result of judgment at stepS19 is NO, that is if the focussing error timeout timer has not timedout, processing transfers to a tenth step S20.

At this tenth step S20, the focussing error signal FE is captured viaA/D port to judge whether or not its signal level is larger than a firstthreshold value T_(—H). If the result of judgment at this tenth step S20is NO, that is if the signal level of the focussing error signal FE issmaller than the first threshold value TH_(—H), processing reverts tothe ninth step S19 to repeat the decision of the timeout of thefocussing error timeout timer. If the result of judgment at the tenthstep s20 is YES, that is if the focussing error signal FE is larger thanthe first threshold value TH_(—H), processing transfers to the eleventhstep S21.

At this eleventh step S21, it is judged whether or not the focussingerror timeout timer has timed out. If the timer has timed out, adetection error is judged to have occurred, and accordingly, processingtransfers to the third step S13 to perform error processing. If theresult of decision at the eleventh step S21 is NO, that is if the timerhas not timed out, processing transfers to the twelfth step S22.

At this twelfth step S22, the focussing error signal FE is captured viaA/D port to judge whether or not its signal level is smaller than asecond threshold value TH_(—L). If the result of decision at this stepS22 is NO, that is if the signal level of the focussing error signal FEis larger than the second threshold value TH_(—L), processing reverts tothe eleventh step S21 to repeat the decision on timeout of the focussingerror timeout timer. If the result of decision at this step S22 is YES,that is if the signal level of the focussing error signal FE is smallerthan the second threshold value TH_(—L), the disc D is judged to be adouble-layer disc in which a S-curve of the focussing error signal FE isdetected twice during the logical ‘H’ period of the disc discriminationsignal DD_(PI), as shown in FIG. 24C. Thus, processing transfers to athirteenth step S23 to set parameters for various circuits associatedwith the double-layer disc.

The first and second threshold values TH_(—H) and TH_(—L) are given as

TH_(—H)=FE_(—o)+W

TH_(—L)=FE−o−W

where W is the width of a detecting window and FE_(—o) is the referencevalue captured at the above step F203.

Thus, as shown in FIG. 24d, even if an offset is caused in the focussingerror signal FE directly entering the A/D input port of the systemcontroller 30, it is cancelled to enable correct disc discrimination.

Thus, with the optical disc device of the present invention, in whichthe closed-loop gain of the automatic power control means is controlledby control means to a gain corresponding to the reflectivity of theoptical disc, based on the detection output of photodetector means whenthe focussing is applied to a signal surface of the optical disc, alaser light beam of an optimum power can be stably illuminated on pluraltypes of optical discs. Thus, stable signals can be read out from theoptical disc by the photodetector means, thus giving playback RF signalswith superior S/N ratio.

By discriminating types of plural optical discs with different numbersof signal recording layers by disc discriminating means based on thefocussing error signals generated by the focussing control means onmoving the objective lens by focussing search by the focussing controlmeans along the optical axis for focussing search, and by setting theoperating mode in meeting with the disc type by the control means basedon the discrimination output, data from plural types of optical discscan be reproduced reliably.

By illuminating laser light on a signal surface of the optical disc viaan objective lens, and by detecting the reflected light of the laserlight from the signal surface of the disc, disc types with differentnumbers of signal recording layers can be discriminated easily based onthe focussing error signals generated from the detection signals.

Since the operating characteristics of the tracking control means can beswitched responsive to the disc types by the control means based on thedecision output of the disc discrimination means, tracking control canbe performed reliably on the plural disc types having differentreflectivities.

Since the operating characteristics of the mirror signal generatingmeans can be switched responsive to the disc types by the control meansbased on the decision output of the disc discrimination means, mirrorsignals can be reliably produced for the plural disc types by the mirrorsignal generating means.

Since the detection system of the tracking control means can beswitch-set responsive to the disc types by the control means based onthe decision output of the disc discrimination means, tracking controlcan be performed reliably on the plural disc types having differentreflectivities.

What is claimed is:
 1. An optical disc device comprising: a laser lightsource for radiating a laser light beam illuminated via an objectivelens on a signal surface of an optical disc; return light detectionmeans for detecting the reflected light radiated from the laser lightsource and reflected from the signal surface of said optical disc; discdiscriminating means for discriminating the type of said optical discbased on a number of reflectivity peaks detected by said return lightdetection means in a sole focussing search operation for focussing saidobjective lens onto said signal surface, said number of reflectivitypeaks corresponding to a same number of signal surfaces that said disccomprises; means for detecting tracking error signals of pluraldifferent types of different detection systems based on the detectionoutput of said return light detection means; tracking means fordisplacing the objective lens along the radius of said optical discresponsive to said tracking error signals for tracking-controlling alaser spot of the laser light focussed on the signal surface of theoptical disc; and controlling means for controlling operation of saidoptical disc device based on a discriminating output by said discdiscriminating means.
 2. The optical disc device of claim 1, wherein afirst disc type is discriminated when only reflectivity peakscorresponding to two signal surfaces are detected in said sole focussingsearch operation.
 3. The optical disc device of claim 2, wherein asecond disc type is discriminated when only one reflectivity peakcorresponding to a single signal surface of said disc is detected duringsaid sole focussing search operation.
 4. The optical disc device ofclaim 1, wherein a first disc type is discriminated when only onereflectivity peak corresponding to a single signal surface of said discis detected during said sole focussing search operation.
 5. A method ofdiscriminating a loaded one of plural types of optical discs for datarecording/reproduction using an optical disc device which includes alaser light source, a light detector, a processor, electricaldiscriminating circuitry, tracking servo and tracking error circuitry,comprising the steps of: radiating a laser light beam illuminated via anobjective lens on a signal surface of an optical disc; detecting theradiated light reflected from a signal surface of said loaded opticaldisc; moving said objective lens in a sole focussing search operationfor focussing said objective lens onto said signal surface such that afocal plane of said lens moves through all signal surfaces of saidloaded optical disc; discriminating which of the plural types of saidoptical discs is the loaded one based on a number of reflectivity peaksdetected in said sole focussing search operation, said number ofreflectivity peaks corresponding to a same number of signal surfacesthat said loaded disc comprises; controlling operation of said opticaldisc device based on discriminating output.
 6. The method of claim 5,wherein a first disc type is discriminated in said discriminating stepwhen two refelectively peaks corresponding to two signal surfaces aredetected in said sole focussing search operation.
 7. The method of claim6, wherein a second disc type is discriminated in said discriminatingstep when only one reflectivity peak corresponding to a single surfaceof said disc is detected during said sole focussing search operation. 8.The method of claim 5, wherein a first disc type is said discriminatedin said discriminating step when only one reflectively peakcorresponding to a single surface of said disc is detected during saidsole focussing search operation.
 9. An optical disc device comprising: alaser light source for radiating a laser light beam illuminated via anobjective lens on a signal surface of an optical disc; a detector fordetecting the reflected light radiated from the laser light source andreflected from the signal surface of said optical disc; a discriminatorcircuit for discriminating the type of said optical disc based on anumber of reflectivity peaks detected by said detector in a solefocussing search operation for focussing said objective lens onto saidsignal surface, said number of reflectivity peaks corresponding to asame number of signal surfaces that said disc comprises; a trackingcircuit for detecting tracking error signals of plural different typesof different detection systems based on the detection output of saiddetector; a tracking servo for displacing the objective lens along theradius of said optical disc responsive to said tracking error signalsfor tracking-controlling a laser spot of the laser light focussed on thesignal surface of the optical disc; and a controller for controllingoperation of said optical disc device based on a discriminating outputby said discriminator circuit.
 10. The optical disc device of claim 9,wherein a first disc type is discriminated when two reflectivity peakscorresponding to two signal surfaces are detected in said sole focussingsearch operation.
 11. The optical disc device of claim 10, wherein asecond disc type is discriminated when only one reflectively peakcorresponding to a single signal surface of said disc is detected duringsaid sole focussing search operation.
 12. The optical disc device ofclaim 9, wherein a first disc type is discriminated when only onereflectively peak corresponding to single surface of said disc isdetected during said sole focussing search operation.
 13. An opticaldisc device comprising: a laser light source for radiating a laser lightbeam illuminated via an objective lens on a signal surface of an opticaldisc; return light detection means for detecting the reflected lightradiated from the laser light source and reflected from the signalsurface of said optical disc; disc discriminating means fordiscriminating the type of said optical disc based on a number ofreflectivity peaks detected by said return light detection means in asole focussing search operation, said number of reflectivity peakscorresponding to a same number of signal surfaces that said disccomprises; means for detecting tracking error signals of pluraldifferent types of different detection systems based on the detectionoutput of said return light detection means; tracking means fordisplacing the objective lens along the radius of said optical discresponsive to said tracking error signals for tracking-controlling alaser spot of the laser light focussed on the signal surface of theoptical disc; and controlling means for controlling operation of saidoptical disc device based on a discriminating output by said discdiscriminating means, wherein a first disc type is discriminated whentwo reflectivity peaks corresponding to two signal surfaces are detectedin said sole focussing search operation.
 14. The optical disc device ofclaim 13, wherein a second disc type is discriminated when only onereflectivity peak corresponding to a single signal surface of said discis detected during said sole focussing search operation.
 15. The opticaldisc device of claim 13, wherein a first disc type is discriminated whenonly one reflectivity peak corresponding to a single signal surface ofsaid disc is detected during said sole focussing search operation.
 16. Amethod of discriminating a loaded one of plural types of optical discsfor data recording/reproduction using an optical disc device whichincludes a laser light source, a light detector, a processor, electricaldiscriminating circuitry, tracking servo and tracking error circuitry,comprising the steps of: radiating a laser light bean illuminated via anobjective lens on a signal surface of an optical disc; detecting theradiated light reflected from a signal surface of said loaded opticaldisc; moving said objective lens in a sole focussing search operationsuch that a focal plane of said lens moves through all signal surfacesof said loaded optical disc; discriminating which of the plural types ofsaid optical discs is the loaded one based on a number of reflectivitypeaks detected in said sole focussing search operation, said number ofreflectivity peaks corresponding to a same number of signal surfacesthat said loaded disc comprises; controlling operation of said opticaldisc device based on discriminating output, wherein a first disc type isdiscriminated in said discriminating step when two reflectivity peakscorresponding to two signal surfaces are detected in said sole focussingsearch operation.
 17. The method of claim 16, wherein a second disc typeis discriminated in said discriminating step when only one reflectivitypeak corresponding to a single signal surface of said disc is detectedduring said sole focussing search operation.
 18. The method of claim 16,wherein a first disc type is discriminated in said discriminating stepwhen only one reflectivity peak corresponding to a single signal surfaceof said disc is detected during said sole focussing search operation.19. An optical disc device comprising: a laser light source forradiating a laser light beam illuminated via an objective lens on asignal surface of an optical disc; a detector for detecting thereflected light radiated from the laser light source and reflected fromthe signal surface of said optical disc; a discriminator circuit fordiscriminating the type of said optical disc based on a number ofreflectivity peaks detected by said detector in a sole focussing searchoperation, said number of reflectivity peaks corresponding to a samenumber of signal surfaces that said disc comprises; a tracking circuitfor detecting tracking error signals of plural different types ofdifferent detection systems based on the detection output of saiddetector; a tracking servo for displacing the objective lens along theradius of said optical disc responsive to said tracking error signalsfor tracking-controlling a laser spot of the laser light focussed on thesignal surface of the optical disc; and a controller for controllingoperation of said optical disc device based on a discriminating outputby said discriminator circuit, wherein a first disc type isdiscriminated when two reflectivity peaks corresponding to two signalsurfaces are detected in said sole focussing search operation.
 20. Theoptical disc device of claim 19, wherein a second disc type isdiscriminated when only one reflectivity peak corresponding to a singlesignal surface of said disc is detected during said sole focussingsearch operation.
 21. The optical disc device of claim 19, wherein afirst disc type is discriminated when only one reflectivity peakcorresponding to a single signal surface of said disc is detected duringsaid sole focussing search operation.